Abstract
OBJECTIVE: To describe a tobacco cessation intervention using personalized mobile phone text messages based on behaviour change theory and to assess why the intervention was effective. METHODS: We conducted a two-arm, double-blind, randomized controlled trial in five cities in China from April to July 2021. We recruited daily or weekly smokers aged 18 years or older. The 90-day intervention was delivered using a mobile phone chat application. At different stages of quitting, intervention group participants received personalized text messages based on analyses of the strength of their intention to quit, their motivation to quit and their self-reported success at quitting. Control group participants received non-personalized text messages. The primary outcome was the biochemically verified 6-month abstinence rate. Secondary outcomes were changes in scores on the components of protection motivation theory. All analyses were by intention to treat. FINDINGS: We randomly assigned 722 participants to intervention or control groups. Biochemically verified continuous abstinence at 6 months was 6.9% (25/360) in the intervention group and 3.0% (11/362) in the control group. Smokers who received the personalized intervention had lower scores on intrinsic rewards of smoking and response costs of quitting in the protection motivation theory analysis. These two variables were also determinants of sustained abstinence, thus explaining why the intervention group had a higher quitting rate. CONCLUSION: The study confirmed the psychological determinants of long-term abstinence from smoking and provided a framework to explore why such an intervention is effective. This approach may be applicable to the development or analysis of interventions targeting other health behaviours.